It's no secret that Google scans your emails to send you targeted ads, but that's not all the search giant is looking for.

Google has developed technology to identify images associated with child porn by looking at the "digital fingerprint" of photos and other attachments that find their way onto Google's servers.

According to Extreme Tech:

Google maintains a database of known indecent images of children — and then compares the hash/fingerprint [of] every attachment you send against that database. If there’s a match, presumably a human at Google double-checks the result and then notifies the relevant authorities.

And that's exactly what Google did in this case. It intercepted child porn from a Houston man's Gmail account, which led to his arrest.

While this technology was used for a good cause, it brings up the always-present issue of what Google is doing with its users' privacy.

Google says that they only use the technology to scan for child porn and that they don't scan for other criminal activity, like if directions on how to murder a person were emailed. That information will need to be taken with a warrant, which a judge recently ruled is legal.